Aphid's Color Comes From a Fungus Gene

Iron Nose writes with an account from Byte Size Biology of horizontal gene transfer from a fungus to an insect. The author suspects that we will see lots more of this as we sequence more genomes. "The pea aphid is known for having two different colors, green and red, but until now it was not clear how the aphids got their color. Aphids feed on sap, and sap does not contain carotenoids, a common pigment synthesized by plants, fungi, and microbes, but not by animals. Carotenoids in the diet gives many animals, from insects to flamingos, their exterior color after they ingest it, but aphids do not seem to eat carotenoid-containing food. Nancy Moran and Tyler Jarvik from the University of Arizona looked at the recently sequenced genome of the pea aphid. They were surprised to find genes for synthesizing carotenoids; this is the first time carotenoid synthesizing genes have been found in animals. When the researchers looked for the most similar genes to the aphid carotenoid synthesizing genes, they found that they came from fungi, which means they somehow jumped between fungi and aphids, in a process known as horizontal gene transfer."

Comments

wiki

[hh4m]

http://en.wikipedia.org/wiki/Horizontal_gene_transfer

Re:wiki

[masterwit]

Carotenoids are colored compounds produced by plants, fungi, and microorganisms and are required in the diet of most animals for oxidation control or light detection. Pea aphids display a red-green color polymorphism, which influences their susceptibility to natural enemies, and the carotenoid torulene occurs only in red individuals. Unexpectedly, we found that the aphid genome itself encodes multiple enzymes for carotenoid biosynthesis. Phylogenetic analyses show that these aphid genes are derived from fungal genes, which have been integrated into the genome and duplicated. Red individuals have a 30-kilobase region, encoding a single carotenoid desaturase that is absent from green individuals. A mutation causing an amino acid replacement in this desaturase results in loss of torulene and of red body color. Thus, aphids are animals that make their own carotenoids.

That's the abstract from the in-text link, whatever a Phylogenetic analyses is...my guess:

Phase 1: Found genes......Phase 2: ???......Phase 3: Science! (good point mrmeval)

Re:wiki

[Anonymous Coward]

...they have not shown where they have observed this happening.

It's like paternity tests: you can't exactly get in a time machine and go observe it happening but when you calculate the probabilities based on reasonable assumptions they can come out pretty high.

Re:wiki

[morty_vikka]

The fact that the genes are identical does not mean they're of the same origin.

Actually, if the genes are identical in terms of nucleotide sequence then it is absolutely irrefutable that they are of the same origin. Even genes that are evolutionarily conserved vary in sequence between members of the same genus, let alone organisms from completely different kingdoms of life.

Re:wiki

[Anonymous Coward]

Well, they can't publish their entire paper in the abstract - the details cost you money, unfortunately. However, it's likely that the method they followed involved statistical comparisons of the nucleotide sequence for similarity. Initially, this seems to be pseudo-scientific, but there are a number of factors to consider: Eukaryotes(animals and fungi + others) make several modifications to the "raw" sequence before translation machinery can code protein from an mRNA template(exons, for example: http://en.wikipedia.org/wiki/Exon). Now, if the coding (post-splice) sequence bears sufficient similarity, you can with fair confidence say that the genes probably have a recent common origin (on the scale of geological time.)
Phylogenetic analysis is basically doing this for a wide array of organisms, essentially looking for the most similar gene in terms of 1:1 exon similarity, then using that data to state with high confidence that this gene in aphids is more related to that gene in fungi than any other potential candidate for the source of this gene.

I knew it!

[masterwit]

As an aside, many of our pseudogenes and other contents of “junk DNA” are thought to have been acquired by horizontal gene transfer.

The guy behind the genetically mutated guido, look at his hand. (I'm sorry you cannot un-see that)

On a more serious note, my roommate, a biology/pre-med major, found this article very interesting and said thanks.

Apparently horizontal gene transfer (or at least inserting useless bits of DNA) is not very hard to do in a lab environment and is very common in bacteria, viruses, and other single celled organisms. Here is another link I found from 08 that talks about bacteria (E.coli) if anyone wants a read http://genomebiology.com/2008/9/1/R4 (full text). Whatever I'm no expert in this field, but I like this type of stuff.

Re:Correlation fallacy, much?

[brusk]

Most knowledge about evolutionary biology is based on evidence like this, and there are lots of ways to be pretty confident about such conclusions, even if there's no way to 100% rule out chance. If this gene and/or others like it are widespread in fungi, that's a hint that it developed in fungi--and under some conditions you might be able to show that the gene evolved in fungi before aphids even existed. Conversely, if no other aphids or related species have anything like this gene, it's a good bet that it came from outside. If the gene evolved suddenly in one lineage of aphids and transferred to a fungus, you would expect only a limited range of fungi, and only those that evolved after aphids did, to have the gene.

Re:Correlation fallacy, much?

[Anonymous Coward]

The transfer definitely did not go in the other direction, as the genes for the carotenoids would have had to travel back up the phylogenetic tree and down its other branches to all the other organisms containing carotenoids. The argument that the aphids evolved genes to express carotenoids in parallel to the part of the phylogenetic tree containing them does not fit into the current model for evolution, as a gene only evolves once, and any other organism containing that gene is descended from the organism that originally mutated to express that gene (this uses statistics and probabilities too!).

Anyway, in almost every science nothing is solidly proven, there are merely theories. Everyone objecting to the validity of this article has been doing too much statistics and not enough biology. You can rest assured the article went under much more intense scrutiny than comparison to a webcomic to get published in Science (no matter how awesome that webcomic is).

Re:Nature's own GMO

[osgeek]

I don't imagine we'd create anything highly adaptable, that's nature's thing.

Genetic tinkerers don't create anything in the "from scratch" sense. They copy complex and fully-formed genes from one life form to another.

It's like using a well-debugged library in a new application.